In C#, How can I reuse an HttpClient for multiple services?

Question

I've created a C# microservice which offers several different (but related) functions.

I am now creating a C# Nuget package for a client which will help other C# microservices to leverage this microservice. This will include a Service Collection Extension class to facilitate adding the client to those microservices.

In the interest of separating concerns, within the client, I've separated the functionality into three classes:

• SalesforceCacheQuerier
• SalesforceCacheSyncDataManipulator
• SalesforceCacheAsyncDataManipulator

Each of these need to call out to the same server.

As a niave first implementation, I've composed this method:

        public static IServiceCollection AddSalesforceClients(this IServiceCollection services)
        {
            services.AddTransient<SalesforceCacheAuthenticationHandler>();
            ConfigureClient(services.AddHttpClient<ISalesforceCacheQuerier, SalesforceCacheQuerier>());
            ConfigureClient(services.AddHttpClient<ISalesforceCacheSyncDataManipulator, SalesforceCacheSyncDataManipulator>());
            ConfigureClient(services.AddHttpClient<ISalesforceCacheAsyncDataManipulator, SalesforceCacheAsyncDataManipulator>());
            return services;
        }

        private static IHttpClientBuilder? ConfigureClient(IHttpClientBuilder? clientBuilder)
            => clientBuilder.ConfigureHttpClient(ConfigureClient)
            .ConfigurePrimaryHttpMessageHandler(() => new SocketsHttpHandler())
            .AddHttpMessageHandler<SalesforceCacheAuthenticationHandler>();

        private static void ConfigureClient(IServiceProvider provider, HttpClient client)
        {
            SalesforceCacheSettings? settings = provider.GetRequiredService<SalesforceCacheSettings>();
            client.BaseAddress = new Uri(settings.BaseUrl, settings.ApiEndpoint);
            client.DefaultRequestHeaders.ExpectContinue = true;
        }

However, this generates three separate HttpClients and triples the traffic for the "Identity Server" used to provide Jwt tokens.

How can I refactor this to create and reuse only a single HttpClient?

Answer 1

What I needed was something like this:

            services.AddHttpClient(SALESFORCE_CACHE_CLIENT, (provider, client) =>
            {
                SalesforceCacheClientSettings? settings = provider.GetRequiredService<SalesforceCacheClientSettings>();
                client.BaseAddress = new Uri(settings.BaseUrl, settings.ApiEndpoint);
                client.DefaultRequestHeaders.ExpectContinue = true;
            })
                .AddHttpMessageHandler<SalesforceCacheAuthenticationHandler>();

            services.AddHttpClient<ISalesforceCacheQuerier, SalesforceCacheQuerier>(SALESFORCE_CACHE_CLIENT);
            services.AddHttpClient<ISalesforceCacheSyncDataManipulator, SalesforceCacheSyncDataManipulator>(SALESFORCE_CACHE_CLIENT);
            services.AddHttpClient<ISalesforceCacheAsyncDataManipulator, SalesforceCacheAsyncDataManipulator>(SALESFORCE_CACHE_CLIENT);